Conserving alfalfa wild relatives: is past introgression with Russian varieties evident today?

Central Asia, particularly Kazakhstan, supports a rich concentration of wild alfalfa (Medicago sativa L.) relatives. Because tetraploid wild alfalfa freely crosses with domesticated alfalfa, they are important genetic resources. When identifying in situ populations to conserve, contamination of wild populations with domesticated alleles is an important consideration. We evaluated population structure and introgression between six wild populations of M. sativa nothossp, varia collected in northwestern Kazakhstan and five traditional Russian cultivars historically grown in the same region using two amplified fragment length polymorphism primer pairs and six simple sequence repeat loci. We found no difference between the Russian cultivars and wild populations for number of alleles or percentage polymorphic loci; however, gene diversity was less in the wild than in the cultivated populations. Cluster analysis and principle component analysis showed clear separation between wild and cultivated populations. Genetic differentiation among the cultivars was less than among the wild populations. Using a Bayesian approach, we found limited evidence of admixture among the wild and cultivated forms, although more admixture was evident in wild populations collected in less-remote areas. On the basis of marker data, we concluded that three of the six wild populations stood out as candidates for in situ conservation given their uniqueness and lack of admixture with cultivated forms.